In conventional dual-compartment refrigerators, a single evaporator fan introduces chilled air into the freezer compartment by blowing air across the evaporator coils of the refrigeration unit. Chilled air is introduced into the fresh food compartment through one or more air passages in a divider wall between the two compartments. An air control device is located within one or more of the air passages to control the flow of chilled air into the fresh food compartment.
Air control devices typically employ a baffle assembly having a fixed plate and a moveable plate which can slide longitudinally relative to the fixed plate between two distinct positions. In a first or open position, a plurality of apertures contained in each plate are aligned, such that chilled air is allowed to flow through apertures and into the fresh food compartment. In a second, or closed position the plurality of apertures are unaligned and blocked, such that the baffle assembly prevents chilled air from flowing into the fresh food compartment when in the closed position. The movement of the movable plate can be controlled by either an electric motor by solenoid coils.
An alternative air control device which does not employ a baffle assembly is a damper assembly having one large opening and a damper to restrict air flow. In a damper assembly, the damper rotates about an axis point along one side. When closed, the damper abuts and covers the opening into the fresh food compartment, impeding the flow of air. When cooling is needed, the damper is rotated to an open position, allow air to flow into the fresh food compartment. The damper is usually controlled by an electric motor attached to the assembly.
Typically, the air passages into the fresh food compartment are located in the back of the compartment, opposite the door. This is mainly because there is more space in the wall at the back of the refrigerator than there is in the sides to accommodate the space requirements of either a damper assembly or baffle assembly. A problem with placement of the air passage in the rear is that since most of the heat entering the fresh food compartment comes through the door when opened, a temperature gradient is created, wherein the back of the fresh food compartment is colder than the front, near the door. It is desirable, therefore, to create air passages in the side walls of the fresh food compartment in order to create a more uniform temperature throughout the fresh food compartment. It is thus desirable to reduce the width of an air control device to allow it to be placed in the thinner side walls of the refrigerator.
The placement of air control devices in the sidewalls close to the door of the fresh food compartment presents a problem regarding the noise level of the device. Current devices, employing either an electric motor or solenoid coils, produce an unacceptable amount of noise to be located near the door. The noise is caused by the electric motors and the solenoids, and by the banging of the movable plates in the baffle assemblies. Some of the noise in baffle assemblies is caused by the excessive amount of force employed to move the baffles. Thus, it is desirable to create an air control device that minimizes the noise produced by its operation.
Some baffle assemblies are constructed with the movable plate connected to one end of an armature and the fixed plate attached to a frame holding two solenoid coils positioned next to each other. The armature is located radially inside the cavities of the solenoid coils. Activation of one of the solenoid coils causes the armature to slide within the solenoid coils' cavities, causing the movable plate to slide longitudinally relative to the fixed plate. The direction of the armature's movements is dependent upon which of the solenoid coils is activated. Alternatively, the armature can be located radially inside the cavity of a single solenoid coil, where opposite electrical charges applied to the solenoid coil cause the armature to move in opposite directions within the solenoid coil's cavity.
In a refrigerator employing one or more air control devices with baffle assemblies as described above, one or more temperature sensors are positioned in various locations of the refrigerator. Each sensor is electrically connected to an air control device. If the baffle assembly is in the closed position and a sensor in the fresh food compartment detects an air temperature at or above a preset level, the sensor sends an electric signal to the baffle assembly to activate one of the solenoid coils, causing the armature to slide the movable plate relative to the fixed plate. As a result, the apertures in the two plates are aligned, thereby allowing chilled air to flow into the fresh food compartment. Likewise, when the baffle assembly is in the open position and the sensor detects an air temperature in the fresh compartment at or below a preset level, an electric signal is sent to the baffle assembly to activate the other solenoid coil, causing the movable plate to slide in the opposite direction. As a result, the apertures become unaligned and blocked, stopping the flow of chilled air to the fresh food compartment.
In order to minimize the amount of time that the solenoid coils remain energized, the system may have a further feature wherein the solenoid coils are deactivated when the temperature sensor detects a change in temperature after initial activation. For example, after the temperature sensor indicates that the air temperature in the fresh food compartment is above the pre-set maximum and the solenoid coil is energized to place the baffle assembly into the opened position, the solenoid coil will remains energized until the temperature sensor detects that the air temperature has stopped increasing. This indicates that the baffle assembly has in fact opened and that chilled air is flowing into the fresh food compartment. The baffle assembly then remains in the opened position after the solenoid coil has been deactivated.
In a conventional refrigerator, moisture at room temperature enters the fresh food compartment when the door of the fresh food compartment is opened. Moisture can accumulate throughout the fresh food compartment, including on the baffle assembly. When chilled air from the freezer compartment subsequently flows through the baffle assembly, the accumulated moisture may freeze, causing ice to form and immobilize the movable plate of the baffle assembly. Consequently, the baffle assembly becomes frozen, making it impossible to regulate the temperature of the fresh food compartment.
The prior art methods for preventing or removing ice on a baffle assembly are expensive and lead to high energy usage. In addition, some of the methods contribute to the premature failure of the solenoid coil. In particular, the currently preferred method uses a solenoid bobbin wherein the cavity created by the solenoid coil has an inside diameter that is larger than the outside diameter of the armature used to slide the movable plate. When the movable plate is idle, ice accumulates between the movable and fixed plates. Upon activation of the solenoid, the accumulated ice initially prevents movement of the plate. However, loose fit of the armature within the solenoid coil allows the armature to move up and down or side-to-side, ultimately breaking the accumulated ice. This additional movement causes added stress to be placed upon the coil while energized, which can lead to premature failure of the coil.
The problem is exacerbated because heat, generated as a natural by-product of energizing solenoid coils, becomes trapped within the solenoid coils. Since the plates are typically not made of a heat-conductive material, the heat does not migrate away from the solenoid coils and instead builds up within the coils. In the prior art described above, the solenoid coils are energized for a longer period because of the need to break free of the ice. The build up of excessive heat is one cause of premature failure of the solenoid coils.
In another prior art method, the solenoid coil periodically and momentarily reverses the direction of the movable plate to prevent the accumulation of ice. Specifically, when the temperature of the fresh food compartment rises above a preset level, the solenoid coil is activated to slide the movable plate to the open position. Once the temperature sensor detects that the temperature has stopped rising, the solenoid coil is deactivated. While in the open position, the solenoid coil is periodically activated to momentarily slide the movable plate into the closed position then immediately returned to the open position to prevent ice from accumulating. Likewise, when the baffle assembly is in the closed position, the solenoid coil is periodically activated to momentarily slide the movable plate into the open position, and then immediately back into the closed position. This method creates unnecessary energy consumption and adds a stress on the solenoid coil as a result of being regularly energized, leading to premature failure of the coils.
In another method, the armature used to slide the movable plate is substantially smaller than the cavity produced by the solenoid coil such that the armature rests within the solenoid coil at an angle. The movable plate rests on top of studs located on the top surface of the fixed plate. Because of the space between the plates created by the studs, any accumulation of ice results in a weak bond. The solenoid coil is periodically energized so that the movable plate maintains its current position and does not slide into another position. When the solenoid coil is energized, the magnetic field generated around the circumference of the angled armature causes the armature to straighten within the solenoid coil. As the angled armature straightens, the movable plate moves outward and away from the fixed plate, thereby breaking the weak ice bonds that had formed between the movable plate and the fixed plate. This method uses an additional amount of energy because the solenoid coils are periodically energized, leading to premature failure of the solenoid coils from the added stress of being regularly energized.
In other prior art methods of eliminating accumulated ice, a resistance wire is molded into the plates. Such an arrangement is shown in Harl, U.S. Pat. No. 4,903,501. The molding process increases the cost of manufacturing the baffle assembly. Additionally, a separate circuit is utilized to heat the plates, which increases the complexity of the air control device, the cost of manufacturing the refrigerator and the amount of energy required.
Still other prior art methods use heaters external to the baffle assembly to prevent the plates from freezing. Such an arrangement is shown in Fujiya, U.S. Pat. No. 4,499,917. This method maintains a plurality of heaters at various points within the baffle assembly which are activated to prevent ice from accumulating on the plates. In this method, an added electric circuit is required for the heaters, increasing the energy usage.
In some cases, it may be desirable to mount an air control device employing a baffle assembly within the refrigerator at an angle other than horizontal. However, depending upon the position of the movable plate relative to the pull of gravity, the solenoid coils may be required to be constantly energized to maintain the movable plate in a position that is subject to the force of gravity, thereby consuming additional energy.
All of these methods for preventing or removing the accumulation of ice increase energy consumption, either by requiring the solenoid coils to be energized more often or for longer periods of time, and/or by the use of heaters. In addition, the solenoid coils may be susceptible to premature failure due to the coils inability to effectively dissipate the heat generated while energized.
The present invention overcomes the problems associated with removing accumulated ice from a baffle assembly in an air control device in a novel fashion. In addition, the invention accomplishes this while using less energy than the prior art.